Madagascar periwinkle is a perennial that readily establishes itself in tropical and subtropical areas to which it is introduced.  Its flowers are probably pollinated by butterflies and moths, as the floral structure is adapted to pollination by a long-tongued insect (Albers and van der Maesen, 1994).  Unlike most species in its family, Madagscar periwinkle is self-compatible; self-pollination may be relatively uncommon in practice, although certain genetic variants have been identified whose floral structure is physically conducive to intraflower self-pollination (Kulkarni et al. 2005).

References

Albers, P. and L. J. G. van der Maesen. 1994. Pollination of Apocynaceae.  Wageningen Agric. Univ. Papers 94-3: 61–81.

Kulkarni, R. N., Y. Sreevalli and K. Baskaran. 2005. Allelic differences at two loci govern different mechanisms of intraflower self-pollination in self-pollinating strains of periwinkle. J. Hered. 96: 71-77.

Sreevalli, Y., K. Baskaran, R. N. Kulkarni and S. Kumar. 2000. Further evidence for the absence of automatic and intra-flower self-pollination in periwinkle. Curr. Sci. 79: 1648-1649.